The long term objective of this research proposal is to obtain a comprehensive understanding of how meiotic recombination caused rapid evolution of gene clusters. This research program will utilize a synthetic RPP1 (synthRPP1) gene cluster to model meiotic recombination in a multicellular organism. Unlike mutant-based genetic screens, the synthRPP1 gene cluster will isolate RPP1 recombinant based on a "gain-of-luciferase" phenotype. This is advantageous because it will identify recombinant RPP1 genes regardless of the RPP1 phenotype. This is a considerable improvement because this approach will isolate recombinant RPP1 genes imparting either neutral or altered phenotypes whereas, mutant phenotype screens only identify recombinant genes with altered phenotypes (mostly loss-of-function). Moreover, this novel procedure provides a high through-put genetic screen for rare recombinant RPP1 alleles in viable progeny. The sampling of millions of viable progeny will provide an accurate estimation of the frequency meiotic unequal crossing-over in any given experiment. This will be particularly useful in experiments that investigate the possible affect of either biotic or abiotic stress on meiotic recombination rates. For example, treatment with either abiotic or biotic stressors (including pathogens) will provide a better understanding of whether or not meiotic recombination is regulated by environmental stress. Mapping of recombination resolution breakpoints will provide important insights into how meiotic recombination affects gene structure (i.e. exon shuffling) or possible mutagenic effects leading to alterations in Leucine Rich Repeat number or composition. Lastly, the recombinant chimeric RPP1 alleles will be tested for new or altered pathogen recognition specificities. Recombinant RPP1 alleles showing altered pathogen recognition profiles will provide new insights into structure-function relationships leading to pathogen recognition specificity. Therefore, this model system will begin to integrate how the molecular details meiotic recombination and R gene structure-function relationships coalesce to result in a measurable and significant increase in the fitness of a multicellular organism.